Method of drying moisture laden articles



April 2, 194e.

W. D. wl-:NGEFel METHOD OF DRYING MOISTURE LADEN ARTICLES Filed May 29, 1945 1&1.

FFI-31:52

lmoentor VViZey D. Wenger l(Ittomeg Patented Apr. 2, 1946 METHOD OF DRYING MOISTURE LADEN ARTICLES Wiley D. Wenger, Camden, N. J., assignor to Radio Corporation ol' America, a corporation of Dela- Ware Application May 29, 1943, Serial No. 489,089

14 Claims.

This invention relates to a method oi drying moisture laden articles, and more particularly to a method of drying thin, sheet-like, dielectric articles by the use of high frequency electric energy.

In the manufacture of thin, sheetdike articles, such as wooden separator plates used in storage batteries, the articles or plates are saturated with certain solutions during their manufacture, and it is necessary to dry them before they can be put to use. Drying methods heretofore generally used have the disadvantage of not drying the articles uniformly throughoutY with the result that the finished articles curl more or less. In case of battery separator plates, when curled separators are placed between the electrodes of "e battery, they often crack and are thereby fridered useless. To overcome this difficulty, the

fparators may be subjected to a high frequency ectric held which would tend to dry them uni- 'oiinly by reason of the dielectric losses which the eld produces therein.

Battery separator plates are usually made with v series of parallel ribs, the ribs at the longitudi- 1:1 ai edges being much Wider than the intermediate bs. If the separators are stacked on top of each rther and the stack is placed between a pair of trodes which terminate a lhigh frequency genor in such relation to the electrodes that the ectroues are parallel to the planes of the sepa- .tors, it is found that the ribs at the edges of 'ie separators reach a higher temperature than he remainder of the plates, and the separator ria-tes therefore do not dry uniformly.

Another difficulty encountered in drying maj'arials by means of a high frequency electrical 'ifeld rather than by applying heat to the work vthrough such means as hot plates or an oven is hat the moisture which is rapidly removed from inside of the material being dried condenses lpon contact with the adjacent electrodes and jfquipment. This condensed moisture retards beating of the outer portion of the material and in many instances results in failure to properly dry materials near the applicator plates or electrodes, thereby causing Waste. It has been pronosed to maintain the moisture in the vaporized state until it is absorbed by the surrounding air by heating the applicator plates or the adjacent parts of the heating units, as by steam or electrical resistance elements. However, to heat the applicator plates and other adjacent parts of the heating apparatus is not desirable since it tends to defeat the purpose of using high frequency heating because it would require that the heating of the electrodes or applicator plates be adjusted separately in accordance with the heat being generated in the material being dried, if best results are to be obtained.

The primary object of my invention is to vprov articles uniformly throughout by means of high frequency electric energy.

Another object of my present invention is to provide an improved method of heating thin, dielectric articles as aforesaid wherein moisture condensation on the surface of the electrodes supplying the high frequency electric eld is avoided.

. Still another object of my invention is to provide an improved method of drying thin, dielectric articles as aforesaid wherein the rapid absorption of the vapor expelled from the material being dried by the surrounding air Will be facilitated so that condensation of the vapor on the applicator electrodes will not take place.

A further object of my invention is to provide an improved method of drying moisture laden, dielectric articles whereby the heating of the material being dried is equalized throughout all parts thereof so that its surface temperature more nearly equals its inner temperature.

It is also an object of my present invention to provide an improved method of drying moisture laden articles as above set forth which is highly efficient and simple to carry out in practice.

In accordance with one feature of my invention, the 1hin separator plates or other similar dielectric articles are stacked in parallel, coaxially aligned relation, and the applicator electrodes are applied thereto in such relation that the electric field set up between the electrodes extends substantially parallel to the planes of the stacked articles. For this purpose, the sheet-like articles may b'e stacked in the direction of their respective, thin dimensions and the electrodes applied thereto along their longitudinal edges. An electrical field set up between the electrodes will then extend in directions parallel to the planes of the stacked arti-cles. Thus, uniform heating throughout each of the articles is assured and therefore the entire stack will be uniformly heated and uniformly dried. y

In accordance with another feature of my invention, and in order to maintain the temperature of the outermost articles of the stack equal to that ferent arrangement for carrying of the inner ones. as well as to assist in the removal of the vaporized or expelled moisture, there may be placed around the articles being dried, or adjacent thereto, one or more layers of moisture absorbing material. For example, 1n the case of the battery separator plates, the separators may be stacked alternately with layers or sheets of blotting paper and as the moisture is driven from the articles being dried, it is forced into the blotting paper or other similar material which has a relatively greater moisture absorbing property than the articles being dried. The absorbing material is preferably also placed Within the electric field and becomes hot in proportion to the moisture driven from the articles being dried. While still in a vaporized state, the moisture is then dissipated into the surrounding air before condensation thereof occurs on the cold parts or the heating equipment. As less moisture is driven from the articles being dried into the absorbing substance, the latter tends to attain the same temperature as that of the articles under treatment, and a point is reached where the inner and surface heat of the articles is substantially the same. This condition is not possible without the use of the moisture absorbing materialbecause of heat conduction by the cold electrodes and the surrounding air, as well-as liquid accumulation on the surface of the articles being dried and on the electrode plates.

The novel features that I consider characteristic of my invention are set forth with particularity inthe appended claims. The inven tion itself, however, both as to its organization and method of operation, as Well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which Figure 1 is a perspective view of one arrangement for carrying out my present invention,

Figure l2 is a sectional-view of a somewhat difout the present invention, and y f Figure 3 is a perspective view of a separator plate of the type to which my present invention is particularly applicable.

Referring more particularly to the'drawing,

wherein similar reference characters designate corresponding parts throughout, there is shown, in Fig. 3, a conventional type of battery separator plate I made of wood or other dielectric material which is more or less moisture absorbent. The separator I is formed with a plurality of parallel ridges or ribs 3 and 5, the ribs 3 along the longitudinal edges of the separator VI being;y relatively wide and the intermediate ribs 5 being relatively narrow. separators of this type are subjected to various treatments with liquids in the course of manufacture, and it is vnecessary to dry them before -they can be put to use. For this purpose, such separators have generally been dried onhot plates or in ovens. Drying by such means causes the separators to curl more or less, and in some instances to such a degree as to render them unfit for use. c

To insure uniform heating and drying of the separators in accordance with the present invention, they are preferably stacked in axially aligned, parallel relation alternately with one or more layers or sheets 'I of moisture absorbent material, such as blotting paper. That is to say,

when the separators I are thus stacked, their principal planes, or the planes of the backsurfaces thereof opposite the ribs 3 and 5 in. each case, are parallel to each other. The longitudinal edges of the separators I are aligned in common, parallel planes normal to the aforesaid principal planes, since the separators all have the same peripheral contours. To further insure against curling, the stack may be confined in a suitable press represented by the press plates 9 `whereby they are maintained in parallel relation, each in its own plane. Sheets of blotting paper or the like la are placed between the separators at each end of the stack and the adjacent presss plates 9. The exposed, longitudinal edges of the separators I may also be covered with layers of blotting paper or the like 1b, and the assembled stack is placed between a pair of electrodes II which are connected through a transformer I3 to a source of radio frequency energy I5, such as a vacuum tube oscillation generator. The electric field set up between the electrodes II will be substantially parallel to the planes of the several separator plates I and of a magnitude sufficient to heat the separators I by reason of the dielectric losses it produces therein to a temperature suiiicient to expel the moisture therefrom.

Since the electric field is uniform throughout, it is apparent that the separators I will be uniformly heated throughout. As the moisture expelled from the articles progresses through the blotters, further evaporation takes place into the air surrounding the blotters. Thus, the moisture at no time reaches the applicator plates to condense into liquid form. At the same time, the heated blotters tend to heat the electrodes II, thereby further reducing the likelihood of moisture condensation. If desired, a suitable blower I1 may be provided to increase the air movement and to force the moisture expelled from the articles I and the blotters 1, la, 'Ib away from the vicinity of the stack. This, however, is not always necessary, particularly where thedrying is carried out at a relatively slow rate.

In the arrangement shown in Fig. 1, the separators I are 'disposed in vertical planes and are stacked in side by side, face to back relation, that is, with the ribs of one separator facing toward the back of the next succeeding one. The separators I or other similar article may, however, be disposed in parallel horizontal planes together with the interposed layers of absorbing material, as shown in Fig. 2. In any case, it is to be noted that the thin articles to be dried are stacked in the direction of their respective thin dimensions and are dried uniformly throughout and therefore they do not curl to any marked degree, if at all.

Although Ihave described my invention in considerable detail, it will, no doubt, be apparent to those skilled in the art that many variations thereof are possible. I therefore desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. The method of drying a relatively thin, sheet-like, moisture-laden, dielectric article with the aid of a moisture absorbent material having a relatively greater moisture absorbing property than said article, which method includes the steps of surrounding said article with said material, and subjecting said article to a high frequency electric field extending substantially parallel to the plane of said article and of a magnitude suilicient to heat said article by reason of the dielectric losses it produces therein to a temperature sufficient to expel the moisture from said article and into said surrounding material.

2. The method of drying a relatively thin, sheet-like, moisture-laden, dielectric article with the aid of a moisture absorbent material, said article being characterized by the tendency to curl while drying and said material being characterized in that it has a relatively greater moisture absorbing property than said article, which method includes the steps of surrounding said article with said material, confining said article to substantially a plane, and subjecting said article while so confined to a high frequency electric field extending substantially parallel to said plane and of a magnitude suiiicient to heat said article by reason of the dielectric losses it produces therein to a temperature sufcient to expel the moisture from said article and into said surrounding material.

3. The method set forth in claim 2 wherein said material is placed in contact with said article. 4. The method set forth in claim 2 wherein said material is placed in contact with said article, and wherein the portions of said material which are in contact with the faces of said article are also conned in planes parallel to that of said article.

5. The invention set forth in claim 2 characterized in that said surrounding material is also subjected to said electric eld whereby to also heat said material-by reason of the dielectric losses produced therein by said field to thereby expel the absorbed moisture from said material.

6. The invention set forth in claim 2 characterized in that said surrounding material is also subjected to said electric eld whereby to also heat said material by reason of the dielectric losses produced therein by said field to thereby expel the absorbed moisture from said material, and characterized further by the additional step of forcing the expelled moisture to move away from the vicinity of said article and said material.

'7. The method of simultaneously drying a plurality of relatively thin, sheet-like, moistureladen, porous, dielectric articles each of nonuniform thickness throughout which includes the steps of stacking said articles in substantially parallel, spaced relation, and subjecting said stacked articles to the influence of a high frequency electric eld extending substantially parallel to the principal planes of said articles, said iield being produced by electrodes adjacent the ends of said articles and being of a magnitude suilicient to heat said articles by reason of the dielectric losses it produces therein to a temperature sufficient to expel the moisture therefrom at a uniform rate throughout said articles to minimize curling thereof.

8. The method of simultaneously drying a plurality of relatively thin, sheet-like, moistureladen, porous, dielectric articles each of nonuniform thickness throughout and each having the same peripheral contour which includes the steps of stacking said articles in substantially parallel, spaced, axially aligned relation, and subjecting said stacked articles to the influence of a high frequency electric iield extending substantially parallel to the principal planes of said articles, said ileld being produced by electrodes adjacent the ends of said articles and being of a magnitude sufficient to heat said articles by reason o1' the dielectric losses it produces therein to a temperature suillcient to expel the moisture therefrom at a uniform rate throughout said articles to minimize 'curling thereof.

9. The method of simultaneously drying a plurality of relatively thin, sheet-like, moistureladen, porous, dielectric articles having a plurality of projections extending from at least one surface thereof which includes the steps of stacking said articles in substantially parallel, spaced, face-to-back relation, and subjecting said stacked articles to the influence of a high frequency electric eld extending substantially parallel to the principal planes of said articles, said field being produced by electrodes adjacent the ends of said articles and being of a magnitude suicient to heat said articles by reason of the dielectric losses it produces therein to a temperature sufficient to expel the moisture therefrom at a uniform rate throughout said articles to minimize curling thereof.

10. The method of simultaneously drying a plurality of relatively thin, sheet-like, moistureladen, porous, dielectric articles each of nonuniform thickness throughout and characterized by the tendency to curl while drying, which method includes the steps of stacking said articles in spaced relation to each other in the direction of their respective, thin dimensions, confining said articles to parallel, principal planes while so stacked, and subjecting said articles while so confined to a high frequency electric field extending substantially parallel to said principal planes, said field being produced by electrodes adjacent the ends of said articles and being of a magnitude suiiicient to heat said articles by reason of the dielectric losses it produces therein to a temperature suilcient to expel the moisture therefrom at a uniform rate throughout said articles to minimize curling thereof.

11. The method of simultaneously-drying a plurality of relatively thin, sheet-like, moistureladen, dielectric articles each of non-uniform thickness throughout with the aid of a moisture absorbent material, which method includes the steps of stacking said articles and layers of said material alternately in parallel relation, and subjecting the stack to a high frequency electric eld extending substantially parallel to the planes of said articles and of a magnitude sumcient to heat said articles by reason of the dielectric losses it produces therein to a temperature suilicient to expel the moisture from said articles into said layers.

12. The method set forth in claim 11 wherein saidJayers are in contact with the adjacent artilcles and wherein layers of said material constitute the outer layers of said stack.

13. The method set forth in claim 11 wherein said layers are also heated by said electric eld to expel the moisture therefrom, and characterized further by the additional step of forcing the moisture expelled from said layers to move away from the vicinity of said stack.

14. The method of drying a moisture-laden, dielectric article with the aid of a moisture absorbent material having a relatively greater moisture absorbing property than said article, which method includes the steps of surrounding said article with said material, and subjecting said article to a high frequency electric eld of a magnitude sufficient to heat said article by reason of the dielectric losses it produces therein to a temperature suicient to expel the moisture from said article and into said surrounding material.

WILEY D. WENGER. 

